Annulate lamellae (AL) are a system of intracellular membranes, frequently observed in rapidly dividing cells in either transformed or embryonic systems. This membraneous network has been the subject of numerous morphological studies, but as yet no attempt has been made to determine the chemical composition or the role that these membranes serve during development and/or transformation. The purpose of this study is to obtain an understanding of the biological significance of these structures. The experiments to be discussed were designed in order to: 1) characterize L membranes, immunochemically, and biochemically; 2) determine the distribution of AL antigens in various cell types, and 3) correlate the expression of AL antigens and membranes with specific cellular activities. These three objectives will be carried out using classical techniques of cell biology. Relatively pure preparation of AL membranes will be fractionated from AL-positive Mouse L cells. The membranes will be characterized by SDS-PAGE and assayed for well known marker enzymes. In addition, the membrane fraction will be used as an antigen in order to generate a library of AL specific antibodies. With the availability of specific probes for AL membranes the presence, distribution, and orgin of these antigens various cells and tissue types will be determined. Finally, experiments have been designed to study the relationship of AL membranes and specific cellular activities, designed to study the relationship of AL membranes and specific cellular activities, e.g. as mitosis. The merit of this proposal rests in its attempt to elucidate a fundamental cellular process that may be instrumental in regulating cell growth and/or differentiation.